Photoresist is a photosensitive material used in semiconductor manufacturing in connection with forming small features in silicon in the process of forming a semiconductor device. As used in photolithography, a silicon wafer is coated with photoresist and placed in the photolithography tool. The particular pattern to be formed in the silicon wafer is embodied in a mask and the mask illuminated. The mask image is projected onto the photoresist, which is sensitive to the wavelength of illumination. The photoresist is then developed so that exposed portions of the photoresist are removed (for “positive” photoresist), leaving a copy of the mask pattern in the photoresist. The patterned photoresist is then etched, which transfers the pattern into the silicon wafer or other material under the photoresist.
Ideally, the photoresist pattern is binary in nature, having perfectly square sidewalls. Moreover, the ideal photoresist is able to replicate the mask image with perfect fidelity and serves as a perfect etch barrier. In practice, photoresist has a limited sensitivity, has some degree of line-edge roughness (LER) and is an imperfect etch barrier.
Efforts have been made to improve photoresist sensitivity, reduce LER and increase the etch resistance. In one case, sequential infiltration synthesis (SIS) is performed using trimethyl aluminum and water at temperatures of less than 100° C. for several minutes to increase etch resistance and reduce LER. This process is described in the publication by Tseng et al., “Enhanced polymeric lithography resists via sequential infiltration synthesis,” J. Mater. Chem., 21, 2011 pp. 11722-25 (also cited as DOI: 10.1039/c1jm12461g).
Unfortunately, the several minutes it takes to carry out this process reduces wafer throughput at the manufacturing line.